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Prickly heat

Published by Bupa’s Health Information Team, August 2011.

This factsheet is for people who have prickly heat, or who would like information about it.

Prickly heat (miliaria) is an itchy, red rash on the skin caused by blocked sweat glands. It's a common condition, particularly in young babies and people who visit hot countries or environments. 

About prickly heat

You can get prickly heat if the sweat glands in your skin become blocked as a result of sweating. It happens when sweat can't escape through the sweat glands and then leaks into the skin layers below. This can cause tiny spots and bumps to appear on your skin. Even if you don't sweat very much, small amounts of sweat can still block your sweat glands and cause prickly heat.

The condition is usually made worse by hot conditions that make you sweat. Prickly heat isn’t an allergy.

Types of prickly heat

There are three types of prickly heat that are classified according to the part of your skin where the sweat glands are blocked.

  • Miliaria crystallina is when the blockage is in the top of the upper layer of your skin (epidermis). This is common in newborn babies as well as in adults who have a fever or who have recently entered a tropical climate.
  • Miliaria rubra happens when the blockage in your sweat gland is in a deeper part of your epidermis. It commonly affects babies (who are one to three weeks old) and adults in hot, humid environments.
  • Miliaria profunda is caused by a blockage in the deep layer of your skin known as the dermis. It’s less common than the other two types of prickly heat. You may get it after having repeated bouts of miliaria rubra.

Prickly heat can occur anywhere on your body, but it usually appears on your neck and torso.

Symptoms of prickly heat

The main symptom of prickly heat is a rash on your skin. Depending on the type of rash you have, it may or may not be itchy.

If you have miliaria crystallina, the rash will usually be made up of small, clear spots. It isn't usually itchy or red. Miliaria crystallina is common in babies, especially on the head, neck and the upper part of the torso. In adults, it usually appears on the torso.

Miliaria rubra causes red spots on your skin, and the skin around the rash is also usually red. It can be very itchy and you may have a prickling sensation on your skin. In babies and young children, the rash usually occurs on the neck, groin and armpits. In adults, the rash often appears in areas where there is friction, such as on your neck and scalp, and the upper part of your chest and back.

Symptoms of miliaria profunda include large spots with a flesh-coloured head. You may also have a prickling sensation on your skin. The rash usually appears on your torso, but you can also have it on your arms and legs.

You may notice that the area of your body affected by the rash doesn't sweat, or you may sweat more in other parts of your body. You may also feel tired and unable to tolerate heat.

You don’t usually need to see your GP if you think you have prickly heat. However, if your symptoms get worse and aren’t improved by self-help measures or over-the-counter creams, see your GP for advice.

Complications of prickly heat

Complications of prickly heat are uncommon. Occasionally, you can develop a bacterial infection.

If you often get prickly heat, you may be more likely to develop heatstroke. This is a serious condition that develops when your body becomes overheated very quickly. The symptoms of heatstroke include headache, dizziness, confusion and a body temperature over 40°C. If this happens, you should seek urgent medical attention as you can become severely dehydrated.

Causes of prickly heat

When you sweat, dead skin cells and bacteria on your skin collect in your sweat glands. If your sweat glands then become blocked, sweat gets trapped underneath your skin and seeps into nearby tissue. This causes inflammation, which appears as a rash.

In babies, prickly heat is thought to be caused by under-developed sweat glands. These glands burst easily when a baby sweats and cause the duct to become blocked.

In adults, the most common cause of prickly heat is being in a hot, humid or tropical environment that you're not used to, or doing activities that make you sweat. You can also get prickly heat in cold environments if you become hot from wearing too many clothes, sit too close to a fire or heater, or get too hot in bed from using thick bedding or an electric blanket. Anything else that blocks your sweat glands can also cause prickly heat. For example, if you wear tight clothing that isn’t breathable, have bandages on your skin, or have to stay in bed because of an illness.

You may be more likely to get prickly heat if you have abnormally high levels of natural bacteria on your skin. For example, the bacteria Staphylococcus epidermidis and Staphylococcus aureus, which usually live on your skin and don’t cause you any harm, may affect your chances of getting prickly heat. People who get prickly heat have three times as many of these bacteria on their skin than people who don’t get prickly heat.

Some medicines, such as neostigmine and bethanechol (used to treat urinary symptoms) and isotretinoin (a treatment for severe acne), may cause prickly heat. This is because these medicines can cause increased sweating as a side-effect.

Diagnosis of prickly heat

You should usually be able to recognise prickly heat from your symptoms. There aren’t any tests for it. However, if you keep getting prickly heat, see your GP for advice. He or she will be able rule out any other conditions that could look similar.

Treatment of prickly heat

Prickly heat usually goes away on its own and doesn't need any treatment. 

Self-help

There are steps you can take to help ease the symptoms of prickly heat. Some examples are listed below.

  • Stick to cooler climates or air-conditioned environments.
  • Try not to wear tight clothing, particularly when you’re doing physical activity,
  • Use an antibacterial soap or antiseptic wash as this may help to reduce the amount of bacteria on your skin.

Medicines

Cooling creams such as those containing menthol or calamine may help if your rash is particularly itchy or uncomfortable. A steroid cream (eg hydrocortisone) may help to soothe any irritation. You can buy this over-the-counter from a pharmacy. If you have miliaria profunda, lanolin creams (eg E45) may improve your symptoms. Always read the patient information leaflet that comes with your medicine and if you have any questions, ask your pharmacist for advice.

Prevention of prickly heat

There are several things you can do to prevent prickly heat, especially if you’re prone to it. 

  • Try not to go to hot, humid environments. If you do, try to become acclimatised to the heat slowly and stick to cool, air-conditioned places as much as possible.
  • Wear loose, lightweight clothing in hot climates.
  • Try not to overexert yourself in hot environments.

Ask your GP for advice if these preventive measures don’t work for you.
 

For answers to frequently asked questions on this topic, see FAQs.

For sources and links to further information, see Resources.

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  • This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the about our health information page.

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  • Publication date: August 2011

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